Dr Paul Allen

NGC 5584 (Photo credit: Wikipedia ) " Billions and billions " of stars in a galaxy (after a quote often mistakenly attributed to Carl Sagan) is how many people imagine the number of stars you would find in one. Is there any way to know the answer for sure? "It's a surprisingly difficult question to answer. You can't just sit around and count stars, generally, in a galaxy," said David Kornreich, an assistant professor at Ithaca College in New York State . He was the founder of the "Ask An Astronomer" service at Cornell University. Even in the Andromeda Galaxy — which is bright, large and relatively close by Earth, at 2.3 million light-years away — only the largest stars and a few variable stars (notably Cepheid variables ) are bright enough to shine in telescopes from that distance. A sun-size star would be too difficult for us to see. So astronomers estimate, using some of the techniques below. Massive investigation The primary way astronomer...

Image via Wikipedia Tim Challies writes: On February 14, 1990, the space craft Voyager 1 was on the very fringe of our solar system. Before it drifted away to wander the galaxy, engineers turned the cameras around and pointed them toward earth, 6.4 billion kilometers away. This historic photograph captured earth as just the tiniest point of light in a vast sky. Carl Sagan looked at that photograph and declared, “Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light.” We are, after all, the inhabitants of just a speck, the tiniest pinprick of light in a universe of unimaginable proportions. How big is the universe? It’s an impossible question for us to answer, of course, but that has not stopped many from making an attempt. I enjoy hearing about those attempts. Here is one that I came across the other day. It’s worth three-and-a-half minutes of your time: Accordi...